Cathode ray tube



y 1940. L. B. HEADRICK 2,202,631

CATHODE RAY TUBE Filed Aug. 20. 1937 NIH INVENTOR L. 5. HEADR/CK BY ATTORNEY Patented May 28, 1940 UNITED STATES CATHOD-E RAY TUBE Lewis Barnard Headrick, Short Hills, N. J., as-

signor to Radio Corporation of America, a corporation of Delaware Application August 20,

4 Claims.

This inventionrelates to cathode ray tubes and more particularly to means for concentrating and focusing the electron ray as produced by the tube.

In many of the systems in which cathode ray tubes at present are used, it is desirable that the ray itself should be of as high a concentration as possible, that is, its cross-sectional area should be as small as possible. These qualifications are particularly desirable when the cathode ray tube is used as an oscilloscope or when used in the transmission or reception of television programs. In the case of the latter, the quality and definition of the picture image as produced by the transmitting tube or Iconoscope or as produced by the television receiver is to a certain extent dependent upon how small the cross-sectional area of the beam can be made at the point at which it strikes the photoelectric mosaic or the fluorescent screen.

In condensing the cathode ray into a very small beam, a series of electrostatic and/or electromagnetic lenses are used and in the use of such lenses a certain amount of spherical aberration has heretofore been present. Because of this spherical aberration it has been difiicult to reduce the cross-sectional area of the beam to the desired degree and it is therefore one purpose of the present invention to provide a gun structure for producing a cathode ray beam wherein the effect of spherical aberration is substantially or completely overcome.

A further purpose of the present invention is to produce a cathode ray tube in which the beam produced by the tube may be. concentrated and focused into a vary small spot.

A still further purpose of the invention is to I Figures 1 and 2 represent examples of the pres- 50 ent or known manner of constructing cathode ray tubes, and

Figures 3 and 4 represent the improved method of constructing cathode ray tubes in accordance with the present invention.

.55 Referring to the drawing, the envelope for con 1937, Serial No. 160,009

taining the cathode ray gun structure is indicated generally at II) in the figures, and may be made of metal, or some vitreous substance such as glass, or in fact any other appropriate mate- I,

rial. Contained within the envelope is a filament element ll which may be heated by any appropriate means and most desirably by electricity for supplying heat to the emitter or cathode element l2. This emitter element is preferably coated with a material which is high in electron emitting quality as is usual in such tubes.

In Figure l the control electrode I3 is shown primarily as an apertured disk which is positioned forward with respect to the emitter. This I electrode is normally maintained negative with respect to the emitter and, by applying varying potentials to this electrode, the intensity of the cathode ray beam may be controlled. Beyond the control electrode I3 is positioned the first accelerating anode 2|, which, in cooperation with the second anode 22, produces a field which causes the cathode ray beam to be focused into a relatively small area. This focusing action is also aided by the differences in potential between the control electrode and the first anode 2! as well as by the current limiting apertures as shown in the first anode. Inthis figure the control electrode 13 aiiects the intensity of the cathode ray beam by the action of the field in the aperture of the control electrode.

In Figure 2 the control electrode 4 is modified slightly in that a skirt portion I5 is provided therefor. The presence of this skirt portion produces a varying field intensity because of the difference in potential between the control electrode and the first anode, which, together with the aperture in the control electrode, determines the intensity and, to a certain degree, the focusing of the produced cathode ray beam. In each of these figures it will be seen that the control electrode is positioned forward with respect to the emitter, and, in each of these tubes, a certain amount of spherical aberration is present.

In Figure 3, and in accordance with this invention, it will be seen that the control electrode l6, together with the skirt portion or cylindrical extension I1, is so positioned that the emitter lies in the plane of the control element, with the activated end portion of the emitter lying entirely within the aperture of the control electrode. Because of this construction, the varying potentials applied to the control electrode affect the cathode ray beam only by the presence of the cylindrical section or skirt l1 and in no way by the field at the aperture per se.

In Figure 4 is shown another form of the invention in which thecontrol electrode I8 includes a cylindrical extension [9 and a frusto-conical member 20. The emitter element is placed in the plane of the small diameter end of the frustoconical member as shown in the figure, and the first anode 2| is positioned forward with respect to the large diameter end of the member, By using a frusto-conical control electrode it is possible, by varying the angle of the conical member 20, to change the field shape and accordingly the control action to give a particular desired control and focusing field. Alsoythe curvature of the field near the cathode or emitter can be made substantially constant over the beam. cross-section. The use of the frusto-conical member results in an elimination of all or substantially all of the spherical aberration that is present to a certain degree in tubes of the usual construction as shown in Figures 1 and 2.

It may be seen from the above that the construction and location of the control electrodes iii in Figure 3 and H3 in Figure 4 difier from that usually employed in cathode ray tubes with the result that the control action of the beam is the result of the presence of the cylindrical section alone as at H in Figure 3 or by the frusto-conical member 2i! as in Figure 4. By eliminating the spherical aberration, as stated above, it is possible to produce better focusing of the beam with the result that the cross section diameter of the beam at the-point of focus, that is, at the point where the beam strikes a photo-sensitive mosaic, a fluorescent screen, or the like, is materially reduced and such reduction, in size permits of increased detail in the image being produced by the beam. It is to be understood that the particular control electrode structure as described above in reference to Figures 3 and 4 in accordance with the present invention, may be used with any appropriate anode structure and that the structiu'e of the first and second anodes as shown in the drawing is only by way of example and may be changed without departing from the spirit of the applicants invention. This is true also with respect to the emitter, since itis only necessary that the emitter, regardless of its type, be placed in the plane of the member which is perpendicular to the axis of the control electrode as shown in Figure 3 or in the plane of the small diameter end of the frusto-conical member as in Figure 4.

It is also to be understood that any specific deflecting means for the cathode ray beam could be used since this forms no part of the applicants invention, and, as a matter of fact, the deflecting means is not shown. Either electro-static or comprising an electron emitter, at least one ac- I celerating electrode and a control electrode; said control electrode being in the form of a frustoconical member and means for coaxially positioning the member between the emitter and the accelerating electrode with the emitter in the plane of the smaller end of the member and with the larger end of the member facing the accelerating electrode.

2. A cathode ray tube including a gun structure for producing a stream of electrons, said structure comprising an electron emitter, at leastone accelerating electrode and a control electrode, said control electrode comprising a centrally perforated disc so positioned that the emitter lies in the plane of the disc and in the perforation thereof, an annular extension attached to the disc in region of the periphery thereof and extending in the direction of the accelerating electrode and a frustro-conical member positioned between the end of the annular extension and the perforation of the disc member.

3. A cathode ray tube, means for producing a stream of electrons comprising an emitter and at least one accelerating electrode, a control electrode positioned between the emitter and the .accelerating electrode, said control electrode being in the form of a frustro-conical member, so positioned that the said emitter lies in the plane of the smaller end ofrsaid member, the larger end of said member facing in the direction of said accelerating electrode.

4. A cathode ray tube, means for producing and focusing a stream of electrons comprising an electron emitter, at least one accelerating electrode and a control electrode, said control electrode being in the form of a frustro-conical memher, and means for positioning said. member betweenthe emitter and the accelerating electrode with the emitter in the plane of the smaller end of the member, and with the larger end facing in the direction of said accelerating electrode, whereby changes in the potential of said control electrode will affect only the intensity of the stream of electrons.

LEWIS BARNARD 

